Oxidation of an Fe-Cr-Al-Y-Zr alloy forming an alumina scale in a Ga2O atmosphere at 1473 K

Abstract

The oxidation of an Fe-Cr-Al-Y-Zr alloy exposed to a Ga atmosphere at 1473 K has been investigated by an encapsulation method. A Ga/Ga 2 O 3 mixture was placed within the quartz ampoules to establish the Ga 2 O and the O 2 partial pressures enveloping a Fe-Cr-Al-Y-Zr alloy (specifically, 72.8Fe-22Cr-5Al-0.1Y-0.1Zr by mass pct), which contains minor additions of yttrium and zirconium to improve scale adherence. A deoxidized Ar atmosphere surrounded the ampoules to control oxygen permeation through the silica wall. The Fe-Cr-Al-Y-Zr alloy developed an Al 2 O 3 scale growing parabolically and protecting the substrate from gallium attack for 5, 10, 20, 40, and 50 days, as examined with a scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analysis. The Ga 2 O atmosphere decomposes to liquid Ga and Ga 2 O 3 on the alloy surface, but gallium species do not penetrate the oxide layer according to the limits of detection for EDX analysis. Defect equilibria incorporating Ga 2 O are presented with neutral interstitial oxygen to explain the oxidation of the Fe-Cr-Al-Y-Zr alloy.